The function of fluoroscopy is to provide a real time imaging mode for various x-ray procedures. Some procedures use the fluoroscopic mode as a means of positioning the recording device through visualization of the internal anatomy of a patient. The recording device will then be presented with the same view as in the fluoro mode, resulting in properly framed images suitable for diagnosis. This type of procedure generally requires a minimal amount of fluoroscopic time, generally less than five minutes. Other procedures use the fluoroscopic mode as the primary mode for positioning instruments within the body, conducting medical intervention, and performing a medical diagnosis of a patient based on the fluoroscopic images. These procedures can be very lengthy and require a lengthy exposure to the x-ray radiation, as long as 2 hours or more.
The optimal x-ray technique used for each of these procedures varies with the type of medical exam being performed and the objective of the exam. For example, vascular procedures typically require kVp settings in the 70 to 90 kVp range for imaging iodinated vessels, whereas gastrointestinal (GI) studies, on the other hand, prefer higher kVp for penetrating barium contrast media. In addition, the technique may also vary as a function of the patient size.
Therefore, a x-ray technique control system that is faced with this multitude of operating situations is preferably designed to accommodate as many of the clinical imaging requirements as possible. The resulting control system then requires knowledge of many aspects of the procedure and patient in order to provide the optimal techniques for each situation.
There are several parameters, or techniques, which are to be controlled in order to effectively accomplish the tasks just outlined. These include kVp, mA, pulse width (exposure time), image quantum noise level (i.e., image receptor entrance exposure or entrance exposure rate). These also include focal spot, x-ray beam spectral quality and patient entrance radiation exposure rate (or Air Kerma). Each of these parameters has an optimal setting, which is unique for each of the procedure demands and patient sizes encountered.
Present control schemes depend on the control of brightness as the mechanism for controlling technique settings. Various methods, usually controlling a single parameter at a time, or having several independent brightness loops, are used to set the technique. Alternate algorithms, which provide better Image Quality control, might be used to allow for several variations in technique trends in controlling brightness but usually a single control parameter dominates the control action.
It would be desirable to have a brightness control system which controls and provides optimal techniques for any clinical application.